1. Field of the Invention
The present invention relates to a file transfer method, a file requesting client device, and a file server device in a system for transferring files from a file server to a file requesting client.
2. Description of the Background Art
In recent years, a system for providing a service of electronic information such as electronic newspapers and electronic publications by utilizing the WWW (World Wide Web) has been widely used. The WWW is a system which provides various files through a network from a WWW server to a WWW viewer which is a client. In the WWW, it is possible to handle files in a format called HTML (HyperText Markup Language), where it is possible to set up a hyperlink from one HTML file to another file. The message exchanges between the server and the client are carried out according to the HTTP (HyperText Transfer Protocol). By utilizing the WWW, files on the WWW servers around the world can be referred from the WWW viewer. In the recent electronic information service, there is an attempt to provide information by charging fee using this WWW.
Here, the file is used as a generic term for all the information which is formed by media such as text, figures, static images, video, audio, etc., and which can be electronically provided. One file may be formed by multiple media.
On the other hand, there is a trend among users to utilize computers in compact sizes. In addition to desktop computers, computers in portable sizes such as laptop computers, notebook computers, PDA (Personal Digital Assistance), etc. are frequently utilized. Unlike the usual desk top computer, the portable terminal is not necessarily used in a state of being connected to a network all the times, and is rather frequently used by being connected to a network according to the need.
In a case of obtaining information by utilizing the WWW from such a computer, it is necessary to keep the portable terminal in a state of being connected to a network until the utilization of the WWW is finished. However, in a case where the portable terminal is connected to a network via a modem, for example, it is desirable to download as much information as possible into the portable terminal first and to view the information content later on after the connection is disconnected.
Also, in future, it is expected that an information server will be placed on a street corner so as to realize a situation in which many people can utilize it to download desired files at desired times into the portable terminal owned by each user for some charge or for free. In such a situation, it is also necessary to make it possible to download the necessary files first, and to view the files later on at places distanced from the information server.
Consequently, for the portable terminal in particular, at a time of obtaining a desired document by connecting the terminal to the network, it is necessary to provide a function which enables references to files similarly as in a case of accessing to the WWW server even in a state where the terminal is disconnected from a network, by downloading not just the desired file but also those files which are likely to be necessary later on into the terminal in advance. This is also an effective scheme for the desk top computer as well, because by downloading files in advance, it becomes possible to display files immediately when a user needs the files.
To this end, it is possible to consider a scheme in which a user explicitly requests necessary files to the server at a time of connecting a computer to a network and downloading a certain file from the server, whenever it is possible to specify the other files which are likely to be necessary later on.
However, when there are many necessary files, it would be necessary for a user to carry out tedious processing. For instance, in a case of electronic newspapers, it is not rare for the newspaper of each day to comprise over one hundred files, and in such a case, it would be necessary for a user to make accesses over one hundred times in order to download all these files.
Thus, in a conventional system for transferring files between the file server and the file requesting client, at a time of downloading a desired file, it has been difficult for the file requesting client or a user using the file requesting client to conveniently specify files related to that desired file which are also to be downloaded.
To sum up the above, in the WWW, a transfer of files from a server to a client is basically carried out file by file. Namely, when a user requests a display of a file such as a document, the WWW client communicates with the WWW server to carry out a transfer of the requested file, and displays the transferred file on a screen. In a case of displaying another file, the same operation is to be repeated again.
However, in a case where the client computer is a computer such as a portable terminal which is not necessarily used under an environment in which it is always possible to connect the terminal to a network, the above scheme is insufficient. In order to provide necessary files to a user immediately in response to a request from a user, it is necessary to transfer multiple files collectively from the server to the client while the client computer is connected with the network, and store the transferred files at the client side.